Figure 4

Composition (a) and morphology (b-e) evolution of the hydrothermal products. The products were obtained at 105°C for different times, with the molar ratio of FeCl₃/H₃BO₃/NaOH = 2:3:4. Time (h) = 1.0 (a₁, b); 3.0 (a₂, c); 6.0 (a₃, d, e). The asterisk represents α-Fe₂O₃ (JCPDS No. 33–0664); nabla represents β-FeOOH (JCPDS No. 34–1266); the bullet represents maghemite (γ-Fe₂O₃, JCPDS No. 25–1402). Inset: high-resolution SEM image of the corresponding sample (c₁).